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  <title>Introduction to Disk Images</title>
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<h2 style="color: rgb(0, 128, 0);">Introduction
to Disk
Images</h2>


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<p>Everyone who once used an
Apple II and now
uses a PC has the same problem: How can you
make
the PC read Apple floppy disks? Unfortunately, without special
hardware, you can't. </p>


<p>Floppy disks are analog
devices, much like
cassette tapes. For a computer to store digital data on a floppy
disk, it must "encode" the data into an analog format.
The Apple II used a method of encoding called Group Code
Recording (GCR), while IBM-compatible PC's used the much more
standard Modified Frequency Modulation (MFM) encoding. Since this
is all done in hardware and cannot be bypassed, it is not
possible for a PC program to "reprogram" the 5.25" floppy
drive in such a way that it could read Apple-formatted floppy diskettes. </p>


<p>Therefore, instead of reading
and writing
disks directly, AppleWin uses disk images. A disk image is a
single file, which you can store on your PC,
which contains all of the data from an entire Apple
diskette. AppleWin treats an image exactly as if it were a real
floppy disk. </p>

<p>Included in the AppleWin distribution is the DOS 3.3 System Master disk dated "January 1, 1983" (<i>DOS 3.3 System Master - 680-0210-A.dsk</i>), a blank DOS 3.3 disk (<i>BLANK.DSK</i>) created using the same System Master disk and a modern ProDOS disk (<i>ProDOS_2_4_3.po</i>).
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NB. ProDOS 2.4 is an updated version by John Brooks, including support for all Apple II's. More details can be found here <a target="_blank" href="https://prodos8.com/">ProDOS8.com</a>. 
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